Metal gasket and method of manufacturing

Abstract

A metal gasket for use in sealing between a cylinder head and a block of an engine includes at least one layer formed with at least one opening therethrough and a deformation feature in the form of a sealing bead, stopper, or both surrounding the opening. The gasket layer is fabricated of austemper-hardenable steel formed when in an annealed state and thereafter austempered to harden the layer and relieve residual forming stresses. During austempering, the layer is supported in a porous fixture that retains the layer against movement out of its plane while permitting it to move within its plane. The fixture has coarse expanded metal exoskeleton liner with wire mesh panels. The mesh liners maintain molten salt against the layers which acts as a thermal cushion to discourage warpage.

I claim:  
     
       1. A metal gasket comprising: 
       at least one metal plate layer having a generally flat, thin planer configuration formed with least one opening therethrough and including a deformation feature projecting from the plane of the layer in surrounding relation to said opening; and  
       said layer being fabricated from austempered steel having a substantially bainitic microstructure.  
     
     
       2. The metal gasket of  claim 1  wherein said layer comprises an active layer of a multi-layer gasket construction and said deformation feature comprises a sealing bead. 
     
     
       3. The metal gasket of  claim 2  wherein said austempered steel comprises low alloy spring steel. 
     
     
       4. The metal gasket of  claim 1  wherein said layer has a predetermined tensile strength and a predetermined fatigue strength, said fatigue strength of equal to about ½ the predetermined tensile strength. 
     
     
       5. The metal gasket of  claim 1  wherein said layer comprises a single layer gasket and said deformation feature comprises a sealing bead surrounding said opening and a stopper surrounding said opening adjacent said sealing bead. 
     
     
       6. The metal gasket of  claim 1  wherein said gasket layer is free of residual stresses imparted from the formation of said deformation feature. 
     
     
       7. A method of making a metal gasket comprising: 
       providing a generally flat thin, gasket layer of austemper-hardenable steel in an annealed condition;  
       forming at least one opening in the layer and deforming the layer out of its plane to provide a deformation feature about the opening; and  
       austempering the formed gasket layer to develop a substantially bainitic microstructure.  
     
     
       8. The method of  claim 7  including supporting the layer in a porous fixture during austempering. 
     
     
       9. The method of  claim 8  including restraining the gasket layer in the fixture against movement out of its plane while permitting the gasket layer to move within its plane. 
     
     
       10. The method of  claim 8  including supporting the gasket layer on opposite sides with rigid porous panels. 
     
     
       11. The method of  claim 10  including directly supporting the gasket layer on either side thereof with inner and outer porous screens, the inner screen having a relatively finer mesh as compared to the outer screen. 
     
     
       12. The method of  claim 10  including supporting the metal layer on opposite sides thereof with a wire mesh panel having between 4 and 16 wires per inch and supporting the wire mesh panels on each side with a porous exoskeleton including relatively coarser panels of expanded metal. 
     
     
       13. The method of  claim 8  including immersing the fixture and gasket layer in a first molten bath and heating both to an austenitizing temperature and thereafter removing the fixture and gasket layer from the first bath and immersing the fixture and gasket layer in an isothermal molten salt bath maintained at an austempering temperature and isothermally transforming the gasket layer from austenite to bainite. 
     
     
       14. The method of  claim 13 , including providing a fine mesh liner in the fixture adjacent the gasket layer and maintaining a protective barrier of molten salt from the first bath within pores of the liner in contact with the gasket layer during transport from the first bath to the isothermal bath. 
     
     
       15. The method of  claim 14  including heating the molten salt barrier during transport with heat from the fixture to maintain the gasket layer at an elevated austenitizing temperature. 
     
     
       16. The method of  claim 7  including relieving the gasket layer of residual forming stresses induced to the layer during formation of the deformation feature.